The invention relates to an amplifier circuit operative with an adaptive signal compression, a signal amplifier being arranged between a signal input and a signal output with a gain factor characteristic curve having a gain factor which is larger and smaller, respectively, below and above a breakpoint, the amplifier being formed with signal combination circuits by which both the breakpoint and the gain factor above the breakpoint are variable for the adaptive signal compression, a smaller gain factor being present above the breakpoint in the case of a higher breakpoint.
A circuit of this type, particularly for use in television is described in U.S. Pat. No. 4,245,237. FIG. 7 of this Patent shows the described gain factor characteristic curve. In addition to the three breakpoints shown for the adaptive signal compression the characteristic curve shows a single breakpoint at a small input signal above which three larger gain factors are present relative to a smaller gain factor therebelow. The three breakpoints for the signal compression occur at one given value of the input signal.
To obtain the described characteristic curve the signal amplifier is formed with the signal combination circuits in the form of subtractor and adder circuits and a non-linear signal processing circuit. Combination of the input signal and the non-linear signal derived therefrom ultimately leads to the output signal to which the described gain factor characteristic curve applies.
In accordance with the said Patent the amplifier circuit described is used to process vertical detail information in a video signal. Signals having small amplitudes are processed with a given gain factor, whilst signals having larger amplitudes are processed with a larger gain factor and signals with the largest amplitudes are processed with a smaller gain factor. In television display it is achieved that for small signal values there is no unacceptable noise in the television picture, whilst the vertical details are displayed in a pronounced manner at mean signal values and the vertical details do not lead to blooming due to the adaptive compression at the highest signal values. As far as the choice of the given gain factor characteristic curve is concerned, the adaptive signal compression can be set by using a variable resistor.